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Pre-ignition screaching!!

875 Views 6 Replies 5 Participants Last post by  ronan95d2
I always wondered what the whirring noise in key position 2 (dash lights on) was. Searching the forum, I discovered that it is the injectors and/or ABS pumps cranking up. Can anyone confirm??

The problem now is that the whirr has turned into loud screach. Any ideas?
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Bearing on the AC fan??
air pump?
is this inside or outside .. bonnet up or not what side what location....we need more detailed you still hear it when you run the motor???
Turn off heater/AC if gone blower bearing. If noise is in dome light with heater on air sampling blower in dome light
Apoogies for the ambiguity guys!

Here's what I can tell you about the noise:-

-intermittent with key in position 2
-coming from the front of the engine compartment.
-still present with A/C off
-disappears (as far as I can hear)when the engine is started.
-sounds a little like an impeller interfering with it's casing
- kicks in and the whirring stops and vice versa.

My guess is root of the problem lies with whatever generates the whirring noise (possibly a bearing here?). Is there a priming pump for air/fuel injectors that cuts out once the engine starts??

Thanks for your input so far. I really want to stay away from the stealers on this one!

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Is the noise coming from the passenger or drivers side of the engine compartment. I also heard a pump kick on with a screechy noise, when i opened the hood i traced it back to the drivers side of the engine compartment, right under the plastic covers. I have no clue what it was though. I hope i get my hands on a manual soon without paying 170 from the dealer for a set of dvds.
I know exactly what you're talking about. I see you have an S280

My C-280 had the same sound. Same 2.8 L inline 6 engine. Sounded like a piece of plastic rattling around. As soon as the service writer at the dealership heard it, he knew exactly what it was. Mine was fixed under Starmark warranty coverage. I don't exactly remember the part, and I don't have the paperwork anymore since I sold the car. I believe it was the throttle flap or something like that. It's a common enough problem. Get it fixed because there is the possibility of plastic parts being sucked through the intake into the cylinders.

Thanks Brett,

As per usual, you seem to be on the money here. Someone put me in contact with a guy who works as a mechanic in one of the MB Stealers in Dublin.

He took a look and said that he has probably come across this once in the last ten years.

The noise is definitely coming from the throttle housing. The engine has also been cutting out occasionally when idling with steering on full lock - both issues point to the need to properly clean out the throttle housing (which is very sensitive).

This guy is going to clean if for me (out of hours, of course!) on Monday and I will let the forum know how it proceeds.
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